Field of the Invention
Preferred and non-limiting embodiments are related to a broken rail detection system and method, and more particularly, to a broken rail detection system and method that utilize information from Communications Based Train Control (CBTC) systems on locations of trains in a train network to detect broken rails.
Description of Related Art
Conventional train signal systems use track circuits for two basic functions: train detection and broken rail detection. In addition, conventional AC coded track circuits are used for track-to-train communications of signal aspect data. The most common type of track circuit used in non-electrified lines is the DC track circuit, which was invented in 1872 and is still widely used today. There are many variations to DC track circuits, including coding to extend lengths and transfer signal information between trackside locations via rails. These variations to DC track circuits use insulated joints to isolate adjacent track circuits. The track circuits are applied to define signal block sections, which are related to signal locations and fixed block train control systems. The signal block sections are used to maintain a safe separation distance between trains.
Audio frequency (AF) track circuits are commonly used in metro signal applications, where shorter headways are required to support trains with shorter stopping distances. AF track circuits are also applied to electrified lines where DC track circuits do not work. AF track circuits do not require insulated joints, but are limited in length due to rail inductance. More specifically, rail inductance typically limits lengths of AF track circuits to about 1 km, as compared to about a 5 km length limit for DC track circuits. Moreover, AF track circuits are more complex and expensive to build and operate than DC track circuits. The combination of increased cost and length limitations render AF track circuits economically impractical for application to lines designed for non-electrified freight traffic.
Heavy haul freight railways predominantly employ continuously welded rail to provide the best rail construction suitable for high axle loads. However, the requirement of insulated joints to use most track circuits, e.g., DC track circuits, for train and broken rail detection results in weak points in the rail, as well as higher maintenance costs. There is thus a clear advantage in minimizing the need for insulated joints, balanced against the economics of alternative solutions.
Communications Based Train Control (CBTC) systems are based upon trains determining and reporting their locations to a control office via radio data communications. A train may also be equipped to monitor its integrity, e.g., to ensure that the train remains connected together as a single unit with a location of each end of the train being known and reported to the control office. CBTC systems may be applied as a moving block configuration, which maintains safe separation distances between trains based upon communications between each of the trains and an office dispatch system. Train separation distances may thus be reduced by the “moving block” configuration based upon train speeds and braking capabilities. When the “moving block” configuration is combined with newer train braking systems, e.g., ECP brakes, braking distances can be further reduced. Safer operation of trains with smaller separation distances therebetween, as well as removal of fixed block and associated wayside signals, can accordingly be supported by CBTC systems.
Conventional CBTC systems can eliminate the need for block track circuits for train detection and associated safe train separation distance functions, but they do not address how to detect broken rail conditions. Conventional track circuits may therefore be applied in addition to the CBTC systems to provide for broken rail protection. In lightly used lines, very long track circuits can be applied, tuned for broken rail detection capabilities, which allow extending lengths to around 8 km. Rail breaks, however, can only be detected by the conventional track circuits when there are no trains in the track circuit section to be tested. If there is a desire to take advantage of CBTC control systems and, operate trains with closer headways, a longer track circuit is often continuously occupied between following trains, leaving no opening to detect rail break conditions in that track circuit. This issue can be addressed by applying shorter DC track circuits, such that there will always be a clear track after a train passes and before the next train occupies the opposite end of each circuit. However, the use of shorter DC track circuits requires adding more wayside equipment locations, which increases costs. Moreover, the use of shorter DC track circuits requires the addition of more insulated joint sections, which also increases costs and lowers reliability.
Conventional track circuits have long been considered as a vital part of train detection. Broken rail detection based on the use of track circuits, however, is only effective when the mechanical rail break also leads to an electrical break in the rail. Rails often fail mechanically, but still maintain a continuous electrical circuit. In some estimates, track circuits successfully detect only about 70% of rail break conditions. This relatively low success rate has led to some railways to abandon use of track circuits for broken rail detection, and to use alternative means for train detection, e.g., axle counters. Heavy haul rail operations with high axle loads, however, typically want to maintain an active means for detecting rail breaks to improve overall rail operations safety. Broken rail detection may thus be considered as part of wayside monitoring systems, similar to dragging equipment and slide fence detectors.
In heavy haul rail operations, almost all rail breaks occur under loaded trains. In most cases, a rail break does not immediately derail the train, but increases risks for the next train to pass that broken section of the rail. It is accordingly advantageous to be able to detect a rail break condition and its approximate location soon after the back end of the train passes the break point.
For conventional rail detection systems using conventional track circuits, if there is a rail break, there is no means to determine the location of the break within the length of the track circuit. The time for railway maintenance to find the break is thus increased.